Changeset 3726 adds two little methods to ActiveSupport: Enumerable#group_by and @ Array#in_groups_of@.

Enumerable#group_by is for collecting an enumerable into sets, grouped by the result of a block. Useful, for example, for grouping records by date.

     latest_transcripts.group_by(&:day).each do |day, transcripts| 
       p "#{day} -> #{transcripts.map(&:class) * ', '}"
     end
     "2006-03-01 -> Transcript"
     "2006-02-28 -> Transcript"
     "2006-02-27 -> Transcript, Transcript"
     "2006-02-26 -> Transcript, Transcript"

Enumerable#group_by will be baked right into Ruby in the future, and currently lives in the 1.9 branch.

Array#in_groups_of let’s you iterate over an array in groups of a certain size, optionally padding any remaining
slots with a specified value (nil by default).

     %w(1 2 3 4 5 6 7).in_groups_of(3) {|g| p g}
     ["1", "2", "3"]
     ["4", "5", "6"]
     ["7", nil, nil]

You gotta love the elegant encapsulation afforded by blocks! Yield.